Laser diode control circuits usually include a well regulated power supply, a feedback photo diode and other circuit components such as operational amplifiers, resistors, capacitors and diodes. Control circuits are generally designed to regulate the light output of a laser diode. This is usually done by comparing the current output of a feedback photo diode, proportional to the light output of the laser diode, to a reference value and appropriately affecting the light output of the laser diode based on the comparison.
For example, U.S. Pat. No. 4,504,976 by Beaudet, assigned to Societe Anonyme De Telecommunications, Paris, issued Mar. 12, 1985, discloses a device for regulating a laser diode, which includes a photo diode for collecting the light power emitted by the laser diode and means for processing the signal derived by the photo diode to control the power emitted by the laser diode. Additionally, U.S. Statutory Invention Registration No. H322 by Simons, assigned to The United States of America as represented by the Secretary of the Navy, issued Aug. 4, 1987, discloses a controller designed to maintain constant laser output power by sampling the light emitted from the laser diode using a detector, amplifying the output of the detector and comparing the amplified output to a reference voltage using an integrator. The output of the integrator controls a series pass transistor that varies the power to the laser diode to provide a constant laser diode output power.
Additionally, laser diode control circuits have been designed to compensate for variations in the power output of a laser diode. For example, U.S. Pat. No. 4,791,632 by Anderson et al, assigned to Sperry Corporation, issued Dec. 13, 1988, discloses a circuit which compensates for changes to the power output of a laser diode which results from temperature variations and aging.
The control circuits discussed above assume that dual and/or well regulated power supplies are used as the supply voltage(s) and/or to operated the laser diode and the active devices contained in the control circuits. For example, U.S. Statutory Invention Registration No. H322 by Simons, discloses a circuit design requiring a power source having +15 and -15 volt capabilities; and U.S. Pat. No. 4,791,632 by Anderson et al, discloses a design requiring a +V and -V power supply. Additionally, none of these control circuits are designed to compensate for variations in the power supply output. Accordingly, the known control circuits are unsuitable for uses requiring a single power supply and are not designed for power supplies whose power output may decrease with age and use (e.g. a battery).
It would be advantageous to eliminate the need for dual, well regulated power supplies by providing a laser diode control circuit designed for a single power supply. It would be desirable to provide a laser diode control circuit which compensates for variations in power output of a single voltage source. It would be desirable to provide a control circuit which maintains a constant laser diode light output despite variations in the power output of a voltage source. It would be advantageous to provide a laser diode control circuit designed to pulse modulate the light output of a laser diode.